. . . Published ahead of Print Medicine & Science in Sports & Exercise ® Published ahead of Print contains articles in unedited manuscript form that have been peer reviewed and accepted for publication. This manuscript will undergo copyediting, page composition, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered that could affect the content. Copyright © 2016 American College of Sports Medicine Running Energy Cost and Spring-Mass Behavior in Young versus Older Trained Athletes PATRÍCIA DIAS PANTOJA 1 , JEAN-BENOIT MORIN 2 , LEONARDO ALEXANDRE PEYRÉ-TARTARUGA 1 , and JEANICK BRISSWALTER 2 1 Exercise Research Laboratory, School of Physical Education, Federal University of Rio Grande do Sul, Porto Alegre, Brazil; 2 Laboratory of Human Motricity, Expertise Sport and Health, University of Nice Sophia Antipolis, Nice, France Accepted for Publication: 11 April 2016 ACCEPTED